Air-cooled igniter plug



Oct. 17, 1950 S E 2,526,169

AIR-000mb IGNITER PLUG Filed Sept. 4, 1948 (Incl-neg:

Patented Oct. 1 7, 1950 AIR-COOLED rcm'rna PLUG Donald J. Steeg,Washington, D. 0., assignor to General Motors Corporation, Detroit,Mich., a

corporation of Delaware Application September 4, 1948, Serial No. 47,858

16 Claims.

This invention has to do with igniters for fuel burners and moreparticularly with igniters generally similar to internal combustionengine spark plugs which are employed to ignite the fuel supplied to thecombustion chambers of combustion gas turbines.

During the operation of combustion gas turbines and other apparatuswhich include fuel burners, the igniter plugs are exposed to the highlyheated products of combustion and, consequently, are maintained at hightemperatures which tends to deteriorate them. Moreover, during theoperation of the apparatus carbon from the fuel is deposited and buildsup in the spaces between the insulators and the shells of the plugs andin and around the spark gaps of the plugs. The build-up of carbon in andaround the spark gaps of the plugs renders the plugs unreliable, if notinoperative, after the apparatus in which they are installed havebeen-in use for a short while.

Frequent removal of the plugs for inspection and/ or cleaning not onlymeans that the apparatus (and the airplanes in which they are installedin the cases of apparatus installed in airplanes) must be taken out ofservice frequently and increases the maintenance cost of the apparatusbut also shortens the lives of the plugs. Moreover, in the cases ofapparatus installed in airplanes, frequent inspection and/ or cleaningof the plugs does not afford adequate insurance that the plugs will beoperative, as it is imperative that they be, at all times when theairplanes in which they are installed arein flight so that, in the casesof pulsating jet engines, the engines will continue to operate and, inthe cases of continuous combustion turbines, the turbines may berestarted if they stall. To cool the plugs and keep them clean in orderto obviate frequent inspection and/or cleaning to insure that the plugswill be serviceable at all times between inspections and/or cleanings,it has been proposed to circulate a r through the spaces between theinsulators and the shells and through and around the spark gaps of theplugs. But insofar as I know, none of the expedients which have beenemployed have satisfactorily done what they were intended to do.

The object of this invention is to provide an igniter plug especiallyfor combustion gas turbines which is so constructed and/r arranged thatmovement of air incident to the operation of the turbine will keep itcool and clean so that frequent inspection and/or cleaning will not benecessary to insure that the plug will remain serviceable at all timesbetween inspections and/or cleanings.

For a better understanding of the nature and objects of this invention,reference is made to the following specification and the accompanyingdrawing in which embodiments of my invention are described andillustrated.

In the accompanying drawing:

Figure 1 is a longitudinal section through a portion of one of thecombustion chambers and associated parts of a continuous combustion gasturbine with an igniter plug constructed and arranged in accordance withmy invention.

Figure 2 is an enlarged side elevation, with parts broken away and insection, of the igniter plug shown in Figure 1 viewed as indicated bythe arrow 2 in Figure 1.

Figure 3 isa section taken on line 3-3 of Figure 2.

Figure 4 is a side elevation of a modification of the igniter plug shownin the preceding figures.

Figure 5 is a section taken on line 55 of Figure 4.

In the drawing, the reference character Ill indicates the generallycylindrical outer shell of one of the combustion chambers of acontinuous combustion gas turbine. Over the inner end of the outer shellHi, there is telescoped the outer end of an adapter it through which airis conducted from the compressor of the turbine into the outer shell.Within the outer shell Ill, there is disposed the generally cylindricalliner [2 of the combustion chamber which is of smaller diameter than andcoaxial with the outer shell so that it is radially spaced therefromthroughout its circumference and through whose wall extend openings 13through which air may enter into it from the space between it and'theouter shell. Over the inner end of the liner, there is secured adome-like head M which extends into the adapter I l'. Into the center ofthe head l4 coaxial with the liner, there extends a fuel nozzle l5 towhich fuel is conducted from without the adapter through a fitting l6which extends through the space between the adapter and the head.

The reference character I! indicates an igniter plug which includes ashell IS with a mounting flange IS on it near what will be referred toas its outer end and an electrode 20 on what will be referred to as itsinner end. Within the shell Hi there is disposed an insulator 2| whichis coaxial with the shell and at a distance from its inner end is seatedon the shell so that gas cannot pass between it and the shell butbetween this zone and the inner end of the shell is spaced radially fromthe shell throughout its circumierence. The insulator 2| extendssomewhat beyond the inner end of the shell Is and in it there isembedded an electrode 22 which extends beyond the inner end of theinsulator but is spaced from the electrode 20 to leave therebetween aspark gap.

Through the wall of the shell is near the outer end of the zone in whichthe insulator is spaced radially from the shell, a bore 22 extends intothe interior of the shell. The bore 22 is disposed at a right angle tobut, as is indicated in Figure 3, its axis is offset laterally from theaxis of shell and the insulator such a distance that while the majorportion of the bore is to one side of the axis of the shell and theinsulator a very minor portion (approximately 2%%) of it is to the otherside of the axis of the shell and the insulator.

The plug I1 is installed in the turbine with the iiange is seated on andsecured to the outer surface of the adapter I I and the portion of itsshell between the flange and its inner end extending through openings inthe adapter and the head ll of the liner i2 and the space between theadapter and the head into the interior of the liner. The bore 23 is solocated lengthwise of the shell that it opens into the space between theadapter and the head at distances from the walls of the adapter and thehead and is so oriented that it faces upstream with its axisapproximately parallel to the direction of flow of air through the spacebetween the adapter and the head at the point at which it opens into it.

When the plug is thus installed and the turbine is operating, relativelycool air from the compressor will enter into the interior of the shellof the plugthrough the bore 22 and pass through the space between theshell and the insulator and over the electrodes 20 and 22 into theinterior of the liner I2. This passage of air through the space betweenthe shell and the insulator and over the electrodes of the plug coolsthe plug and prevents or, at least, inhibits the deposition oraccumulation of carbon from the fuel in the space 4 that both theincrease in the rate and theehange in the pattern of the flow of the airthrough the plug and over the electrodes contribute to the increase inthe effectiveness of a bore formed and disposed as shown in Figures 1, 2and 3 and hereinbefore described in cooling the plug and keeping it freeof carbon deposits. The pattern of flow of the air through the plug andover the electrodes especially in the matter of the pitch of the helicalpath of the air, is affected by the proportion of the volume of the airwhich enters the shell that passes to one and the other side of theinsulator and, consequently, by the extent to which the bore is oflsetlaterally of the axis of the shell and the insulator. The rate of flowof air through the plug and over the electrodes is affected by thisfactor and by the size of the bore.

between the shell and the insulator and in and around the spark gap.

Experience has shown that a bore formed and disposed as shown in Figures1, 2 and 3 and hereinbefore described, is much more eflective in coolingthe plug and keeping it free of carbon deposits than a radial hole whichfaces upstream with its axis parallel to the direction of flow of air bythe plug. The reason for this is that with the radial hole air whichenters the shell of the plug is split by the insulator into two streamsof approximately equal volume and force which collide and produce on theside of the insulator opposite that on which the air enters the shelleddies which impede the flow of air through the space between theinsulator and the shell. With a bore formed and disposed as shown inFigures 1, 2 and 3 and hereinbefore described, more of the air whichenters the shell passes to one than the other side of the insulator andthe air within the shell, consequently, eddies less. Moreover, thesmaller stream of air deflects the larger stream toward the inner end ofthe plug and the air which enters the shell, consequently, tends tofollow a hellcal path through the space between the insulator and theshell and over the electrodes. Because of this change in the pattern offlow of the air, the air flows more freely through the plug and its rateof flow therethrough and over the electrodes is, consequently,increased. ,1 consider The pattern and rate of flow of air through theplug and over the electrodes, consequently, can be changed by changingthe extent to which the bore is oflset laterally of the axis of theshell and the insulator and/or the size of the bore and should beadJusted to secure the optimum cooling and cleaning eilect that can beobtained without establishing a pattern or rate of flow of air over theelectrodes which will interfere with the maintenance of a combustiblemixture at this point.

The importance in the matter of increasing the rate of flow of airthrough the plug of eliminating even slight impediments to the flow ofair therethrough becomes apparent when the rel atively large areaofiered by the openings I 2 in the liner as alternative paths for thepassage of air from the space between the outer shell and the liner intothe liner of the combustion chamber and the small differentialbetweenthe pressure of the air in the space between the outer shell andthe liner and the pressure of the gases in the liner of the combustionchamber are considered.

The effect obtained by forming and disposing the bore in the wall of theshell of the plug as shown in Figures 1, 2 and 3 and hereinbei'oredescribed can be obtained with a radial bore in the wall of the shell ifthe bore is oriented so that it faces upstream with its axis at such anangle to the direction of flow of the air through the space between theshell and the liner of the combustion chamber at the point at which thebore is located that more of the air which enters the shell through thebore passes to one than to the other side of the insulator.

In Figures 4 and 5 there is shown an igniter plug 24 in which myinvention in the modified form suggested in the next preceding paragraphis incorporated. The plug 24 includes a shell 25, a mounting flange 28,an insulator 21 and electrodes 28 and is arranged in the same generalmanner as the corresponding parts of the plug l1 shown in Figures 1, 2and 3 and was designed for installation in a continuous combustion gasturbine with a combustion chamber generally like that shown in Figure 1in a manner similar to that in which the plug i1 is installed. However,the ratio of the diameter of the bore 30 to the diameter of the shell ofthe plug 24 is somewhat reater than the ratio of the diameter of thebore 22 to the diameter of the shell of the plug l1 and the axis of thebore- 20, instead of nonradial, is radial to the axis of the shell and,when the plug 24 is installed in the turbine, the

bore II is oriented so that its axis is at such an angle, which isindicated by the double-headed arrow in Figure 5, instead of parallel,to'the direction of flow of air at the point at which the bore islocated that more (approximately 78%) 8oitheopenareapresentedbytheboreatarlsht angle to the direction of flowof the air at the point at which the bore is located lies to one than tothe other side of the axis of the shell and the insulator but a smallerproportion (approximately 22%) lies to the other side of the axis of theshell and the insulator.

Although I have described and illustrated my invention as it has beenapplied to continuous combustion gas turbines. it is to be understoodthe insulator.

that the invention is also applicable to other types a of combustion gasturbines and to other apparatus in which igniters are or may besimilarly installed.

I claim:

1. In a continuous combustion gas turbine combustion chamber, a shellthrough which air travels, a shell-like liner within and spaced from thewall of the shell so that air can pass between it and the shell withopenings in its wall through which air may pass into the liner from thespace between it and the shell, a head over the end of the liner whichis upstream of the flow of air through the shell, and an electricigniter which includes a shell which extends from without the shell ofthe combustion chamber, through the space between the shell of thecombustion chamber and the liner and terminates within the liner, aninsulator in which is embedded an electrode which is disposed within andextendslengthwise of and is spaced from the wall of the shell of theigniter, and an opening in the wall of the shell of the igniter whichopens into the space between the shell of the combustion chamber and theliner upstream of the flow of air therethrough and is offset laterallyof the direction of flow of air through the space between the shell ofthe combustion chamber and the liner from the axis of the insulator sucha distance that the major portion of the opening is to one side of theaxis of the insulator and a minor portion of the opening is to the otherside of the axis of the insulator.

2. The continuous combustion gas turbine combustion chamber claimed inclaim 1 in which the axis of the opening in the shell of the igniter isapproximately parallel to the direction of flow of air through the spacebetween the shell of the combustion chamber and the liner.

3. The continuous combustion gas turbine combustion chamber claimed inclaim 1 in which the axis of the opening in the shell of the igniter isdisposed at an angle to the direction of flow of air through the spacebetween the shell of the combustion chamber and the liner.

4. In a continuous combustion gas turbine combustion chamber, a shellthrough which air travels, a shell-like liner within and spaced from thewall of the shell so that air can pass between it and the shell withopenings in its wall through which air may pass into the liner from thespace between it and the shell, a head over the end of the liner whichis upstream of the flow of air through the shell, and an electricigniter which includes a shell which extends from without the shell ofthe combustion chamber, through the space between the shell of thecombustion chamber and the liner and terminates within the liner, aninsulator in which is embedded an electrode which is disposed within andextends lengthwise of and is spaced from the wall of the shell of theigniter, and an opening in the wall of the shell of the igniter whichopens into the space between the shell of the combustion chamber and theliner upstream of the flow of air therethrough and is oil'set laterallyof the direction of flow of air through the space between the shell ofthe combustion chamber and the liner from the axis of v 5. Thecontinuous combustion gas turbine combustion chamber claimed in claim 4in which the axis of the opening in the shell of the igniter isapproximately parallel to the direction of flow of air through the spacebetween the shell of the combustion chamber and the liner.

6; The continuous combustion gas turbine combustion chamber claimed inclaim 4 in which the axis of the opening in the shell of the igniter isdisposed at an angle to the direction of flow of air through the spacebetween the shell of the combustion chamber and the liner.

7. In a fuel burner, a duct through which air travels, an electricigniter which includes a shell which extends transversely of thedirection of travel of air through and terminates within the duct, anelectrode \which is disposed within and extends lengthwise :of and isspaced from the wall of the shell, and an opening in the wall of theshell which opens into the duct upstream of the flow of air therethroughand is ofiset laterally of the direction of flow of air through the ductfrom the axis of the electrode such a distance that the major portion ofthe opening is to one side of the axis of the electrode and a minorportion of the opening is to the other side of the axis of theelectrode.

8. The fuel burner claimed in claim 7 in which the axis of the openingin the shell is approximately parallel to the direction of flow of airthrough the duct.

9. The fuel burner claimed in claim 7 in which the axis of the openingin the shell is disposed at an angle to the direction of flow of airthrough the duct.

10. In a fuel burner, a duct through which air shell which opens intothe duct upstream of the flow of air therethrough and is offsetlaterally of the direction of flow of air through the duct from the axisof the electrode.

11. The fuel burner claimed in claim 10 in which the axis of the openinin the shell is approximately parallel to the direction of flow of airthrough the duct.

12. The fuel burner claimed in claim 10 in which the axis of the openingin the shell is disposed at an angle to the direction of flow of airthrough the duct.

13. In a fuel burner, a duct through which air travels, an electricigniter including a shell extending transversely of the direction oftravel of air through the duct, means'disposed lengthwise of and in theshell and spaced from its wall, and means for eilecting flow of air in ahelical path about the first-named means, the secondnamed meansincluding an opening in the wall of the shell which opens into the ductupstream of the ficw of air therethrough and is offset laterally of thedirection of flow of air through said duct.

14. In an igniter, a shell, an insulator in which is embedded anelectrode which is disposed within and extends lengthwise of and isspaced from the wall of the shell, and an opening in the wall of theshell whose axis is oilest laterally from the axis of the insulator sucha distance that the major portion or the opening is to one side the axisof the insulator and a minor portion of the opening is to the other sideof the axis of the insulator.

15. In an igniter, a shell, an insulator in which is embedded anelectrode which is disposed within and extends lengthwise of and isspaced from the wall of the shell, and an opening in the wall of theshell whose axis is ofiset laterally from the axis of the insulator.

16. In an improved igniter for use in combustion apparatus having spacedinner and outer walls forming a combustion chamber surrounded by apassage through which air supplied to said combustion chamber flows in aselected direction and also having nozzle means for injecting fuel intosaid combustion chamber, said igniter comprising a tubular body adaptedto be secured to the outer wall of said combustion apparatus and toproject through aligned openings in said outer and inner walls and toterminate within said combustion chamber, an insulator positionedconcentrically within said tubular body, said insulator extendinglengthwise of said tubular body and having adjacent the end of saidtubular body within said combustion chamber a portion spaced from theinner face of said tubular member, and electrodes carried by saidtubular body and by said insulator defining a spark gap located withinsaid combustion chamber when said igniter is in position on saidcombustion apparatus, said tubular body having in the wall thereof anopening which communicates with the interior of said 8 tubular body at apoint where said insulator is spaced from the inner face of said tubularbody. said opening in said tubular body being located so that when saidigniter is in position on said combustion apparatus the opening isintermediate the inner and outer walls of said combustion apparatus andfaces the direction from which air is supplied to the passage betweensaid inner and outer walls, the opening in said tubular body also beingof such size and being disposed so that when said igniter is in positionon said combustion apparatus said opening is oflset from the axis ofsaid insulator laterally of the direction of flow of air through thepassage between said outer and inner walls so that a major portion ofthe area of said opening is at one side of the axis of said insulatorand so that at least a minor portion of the area of said opening is atthe other side of the axis of said insulator.

DONALD J. STEEG.

REFERENCES CITED The following references are of record in the the ofthis patent:

UNITED STATES PATENTS Number v Name Date 2,205,983 Kraber June 25, 19402,465,092 Harkness et a1 Mar. 22, 1949 FOREIGN PATENTS Number CountryDate 587,564 Great Britain Apr. 30, 1947

